A conventional light exposing device is schematically illustrated in FIG. 1. In the device of FIG. 1, a light source assembly 20' is disposed at the bottom of a cabinet 10. A mount 11, mounting a panel 60, is provided at the upper position of the cabinet 10. A correcting filter 13 and a correcting lens 12, for correcting the light radiated from the light source assembly, are disposed between the light source assembly body 20' and the panel 60.
Additionally, a shutter (not shown) is provided, between the correcting lens and filter 12, 13 and the bottom of the panel, for partially passing the light radiated from the light source assembly 20'.
The light source assembly 20' generally takes a form which is the same as or similar to that illustrated in FIG. 2. That is, a light exposing lamp 21' is installed in such a manner as to be exposed to a cavity 23' formed at the center of the body of a cooling tank 22'. A protecting glass 24' may be installed in the middle cavity 23'.
The amount and path of the outgoing light radiated from such a light source assembly may be properly corrected by passing it through the correcting lens and filter, so that the fluorescent stripe on the inner face of the panel should be formed in a uniform manner.
However, there is a limit in the correcting function of the correcting lens and filter. Therefore, in the case of large cathode ray tubes and the like, the light amount exposed on the peripheral areas of the screen may be significantly insufficient relative to the middle area of the screen, resulting in the widths of the fluorescent stripes being non-uniform. This in turn causes an increase in the difference of the luminances in some parts of the screen, thereby lowering the image quality. That is, in the case of a large screen, the difference of the light exposing amounts between the peripheral areas and the middle area of the screen becomes large, giving rise to the above described problems. Increasing the light exposing amount radiated to the peripheral areas of the screen is required to solve the above described problem.